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By NASA
Technicians work to complete operations before propellant load occurs ahead of launch for NASA’s Europa Clipper spacecraft inside the Payload Hazardous Servicing Facility at the agency’s Kennedy Space Center in Florida on Tuesday, Sept. 11, 2024. NASA/Kim Shiflett NASA’s Europa Clipper mission moves closer to launch as technicians worked on Wednesday, Sept. 11, inside the Payload Hazardous Servicing Facility to prepare the spacecraft for upcoming propellant loading at the agency’s Kennedy Space Center in Florida.
The spacecraft will explore Jupiter’s icy moon Europa, which is considered one of the most promising habitable environments in the solar system. The mission will research whether Europa’s subsurface ocean could hold the conditions necessary for life. Europa could have all the “ingredients” for life as we know it: water, organics, and chemical energy.
Europa Clipper’s launch period opens on Thursday, Oct. 10. It will lift off on a SpaceX Falcon Heavy rocket from Kennedy’s Launch Complex 39A. The spacecraft then will embark on a journey of nearly six years and 1.8 billion miles before reaching Jupiter’s orbit in 2030.
The spacecraft is designed to study Europa’s icy shell, underlying ocean, and potential plumes of water vapor using a gravity science experiment alongside a suite of nine instruments including cameras, spectrometers, a magnetometer, and ice-penetrating radar. The data Europa Clipper collects could improve our understanding of the potential for life elsewhere in the solar system.
Photo credit: NASA/Kim Shiflett
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By NASA
Figure 1. An artist’s concept of the Van Allen belts with a cutaway section of the giant donuts of radiation that surround Earth. Image Credit: NASA Goddard Space Flight Center/Scientific Visualization Studio A new instrument is using advanced detection techniques and leveraging an orbit with specific characteristics to increase our understanding of the Van Allen belts—regions surrounding Earth that contain energetic particles that can endanger both robotic and human space missions. Recently, the instrument provided a unique view of changes to this region that were brought on by an intense magnetic storm in May 2024.
The discovery of the Van Allen radiation belts by the U.S. Explorer 1 mission in 1958 marked a prominent milestone in space physics and demonstrated that Earth’s magnetosphere efficiently accelerates and traps energetic particles. The inner belt contains protons in the MeV (million electric volt) to GeV (109 electric volt) range, and even higher concentrations of energetic electrons of 100s of keV (1000 electric volt) to MeV are found in both the inner belt and the outer belt.
The energetic electrons in these belts—also referred to as “killer electrons”—can have detrimental effects on spacecraft subsystems and are harmful to astronauts performing extravehicular activities. Understanding the source, loss, and varying concentrations of these electrons has been a longstanding research objective. High-energy resolution and clean measurements of these energetic electrons in space are required to further our understanding of their properties and enable more reliable prediction of their intensity.
Overcoming the challenges of measuring relativistic electrons in the inner belt
Measuring energetic electrons cleanly and accurately has been a challenge, especially in the inner belt, where MeV to GeV energy protons also exist. NASA’s Van Allen Probes, which operated from 2012 to 2019 in low inclination, geo-transfer-like orbits, showed that instruments traversing the heart of the inner radiation belt are subject to penetration by the highly energetic protons located in that region. The Relativistic Electron Proton Telescope (REPT) and the Magnetic Electron and Ion Spectrometer (MagEIS) instruments onboard the Van Allen Probes were heavily shielded but were still subject to inner-belt proton contamination.
To attempt to minimize these negative effects, a University of Colorado Boulder team led by Dr. Xinlin Li, designed the Relativistic Electron Proton Telescope integrated little experiment (REPTile)—a simplified and miniaturized version of REPT—to fly onboard the Colorado Student Space Weather Experiment (CSSWE). An effort supported by the National Science Foundation, the 3-Unit CSSWE CubeSat operated in a highly inclined low Earth orbit (LEO) from 2012 to 2014. In this highly inclined orbit, the spacecraft and the instruments it carried were only exposed to the inner-belt protons in the South Atlantic Anomaly (SAA) region where the Earth’s magnetic field is weaker, which greatly reduced the time that protons impacted the measurement of electrons.
REPTile’s success motivated a team, also led by Dr. Xinlin Li, to design REPTile-2—an advanced version of REPTile—to be hosted on the Colorado Inner Radiation Belt Experiment (CIRBE) mission. Like CSSWE, CIRBE operates in a highly inclined low-Earth orbit to ensure the exposure to damaging inner-belt protons is minimized. The team based the REPTile-2 design on REPTile but incorporated two additional technologies—guard rings and Pulse Height Analysis—to enable clean, high-energy-resolution measurements of energetic electrons, especially in the inner belt.
Figure 2: PI observing two engineers testing the interface between the CIRBE bus and REPTile-2 on September 29, 2021. Image Credit: Xinlin Li, University of Colorado Boulder As shown on the left in Figure 3, the field of view (FOV) of REPTile-2 is 51o. Electrons and protons enter the FOV and are measured when they reach a stack of silicon detectors where they deposit their energies. However, very energetic protons (energy greater than 60 MeV) could penetrate through the instrument’s tungsten and aluminum shielding and masquerade as valid particles, thus contaminating the intended measurements. To mitigate this contamination, the team designed guard rings that surround each detector. These guard rings are electronically separated from the inner active area of each detector and are connected by a separate electric channel. When the guard rings are triggered (i.e., hit by particles coming outside of the FOV), the coincident measurements are considered invalid and are discarded. This anti-coincidence technique enables cleaner measurements of particles coming through the FOV.
Figure 3. Left (adapted from Figure 1 of Khoo et al., 2022): Illustration of REPTile-2 front end with key features labeled; Right: REPTile-2 front end integrated with electronic boards and structures, a computer-aided design (CAD) model, and a photo of integrated REPTile-2. Image Credit: Xinlin Li, University of Colorado Boulder To achieve high energy resolution, the team also applied full Pulse Height Analysis (PHA) on REPTile-2. In PHA, the magnitude of measured charge in the detector is directly proportional to the energy deposited from the incident electrons. Unlike REPTile, which employed a simpler energy threshold discrimination method yielding three channels for the electrons, REPTile-2 offers enhanced precision with 60 energy channels for electron energies ranging from 0.25 – 6 MeV. The REPT instrument onboard the Van Allen Probes also employed PHA but while REPT worked very well in the outer belt, yielding fine energy resolution, it did not function as well in the inner belt since the instrument was fully exposed to penetrating energetic protons because it did not have the guard rings implemented.
Figure 4: The CIRBE team after a successful “plugs-out” test of the CIRBE spacecraft on July 21, 2022. During this test the CIRBE spacecraft successfully received commands from ground stations and completed various performance tests, including data transmission back to ground stations at LASP. Image Credit: Xinlin Li, University of Colorado Boulder CIRBE and REPTile-2 Results
CIRBE’s launch, secured through the NASA CubeSat Launch Initiative (CSLI), took place aboard SpaceX’s Falcon 9 rocket as part of the Transporter-7 mission on April 15, 2023. REPTile-2, activated on April 19, 2023, has been performing well, delivering valuable data about Earth’s radiation belt electrons. Many features of the energetic electrons in the Van Allen belts have been revealed for the first time, thanks to the high-resolution energy and time measurements REPTile-2 has provided.
Figure 5 shows a sample of CIRBE/REPTile-2 measurements from April 2024, and illustrates the intricate drift echoes or “zebra stripes” of energetic electrons, swirling around Earth in distinct bunches. These observations span a vast range across the inner and outer belts, encompassing a wide spectrum of energies and electron fluxes extending over six orders of magnitude. By leveraging advanced guard rings, Pulse Height Analysis (PHA), and a highly inclined LEO orbit, REPTile-2 is delivering unprecedented observations of radiation belt electrons.
Figure 5: Color-coded electron fluxes detrended between REPTile-2 measurements for a pass over the South Atlantic Anomaly region on April 24, 2023, and their average, i.e., the smoothed electron fluxes using a moving average window of ±19% in energy; Black curves plotted on top of the color-coded electron fluxes are contours of electron drift period in hr. The second horizontal-axis, L, represents the magnetic field line, which CIRBE crosses. The two radiation belts and a slot region in between are indicated by the red lines and arrow, respectively. Image Credit: Xinlin Li, University of Colorado Boulder In fact, the team recently announced that measurements from CIRBE/REPTile-2 have revealed a new temporary third radiation belt composed of electrons and sandwiched between the two permanent belts. This belt formed during the magnetic storm in May 2024, which was the largest in two decades. While such temporary belts have been seen after big storms previously, the data from CIRBE/REPTile-2 are providing a new viewpoint with higher energy resolution data than before. Scientists are currently studying the data to better understand the belt and how long it might stick around — which could be many months.
PROJECT LEAD
Dr. Xinlin Li, University of Colorado Laboratory for Atmospheric and Space Physics and Department of Aerospace Engineering Sciences.
SPONSORING ORGANIZATIONS
Heliophysics Flight Opportunities for Research & Technology (H-FORT) program, National Science Foundation
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Last Updated Sep 17, 2024 Related Terms
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A group of 18 personnel from the 4th Space Operations Squadron, a component of Delta 8, headquartered at Peterson Space Force Base, Colorado, recently traveled to Joint Base Pearl Harbor Hickam, Hawaii for a contingency operations exercise to test a highly technical piece of equipment known as a Mobile Constellation Control Station.
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By NASA
5 min read
Voyager 1 Team Accomplishes Tricky Thruster Swap
A model of NASA’s Voyager spacecraft. The twin Voyagers have been flying since 1977 and are exploring the outer regions of our solar system. NASA/JPL-Caltech The spacecraft uses its thrusters to stay pointed at Earth, but after 47 years in space some of the fuel tubes have become clogged.
Engineers working on NASA’s Voyager 1 probe have successfully mitigated an issue with the spacecraft’s thrusters, which keep the distant explorer pointed at Earth so that it can receive commands, send engineering data, and provide the unique science data it is gathering.
After 47 years, a fuel tube inside the thrusters has become clogged with silicon dioxide, a byproduct that appears with age from a rubber diaphragm in the spacecraft’s fuel tank. The clogging reduces how efficiently the thrusters can generate force. After weeks of careful planning, the team switched the spacecraft to a different set of thrusters.
The thrusters are fueled by liquid hydrazine, which is turned into gases and released in tens-of-milliseconds-long puffs to gently tilt the spacecraft’s antenna toward Earth. If the clogged thruster were healthy it would need to conduct about 40 of these short pulses per day.
Both Voyager probes feature three sets, or branches, of thrusters: two sets of attitude propulsion thrusters and one set of trajectory correction maneuver thrusters. During the mission’s planetary flybys, both types of thrusters were used for different purposes. But as Voyager 1 travels on an unchanging path out of the solar system, its thruster needs are simpler, and either thruster branch can be used to point the spacecraft at Earth.
In 2002 the mission’s engineering team, based at NASA’s Jet Propulsion Laboratory in Southern California, noticed some fuel tubes in the attitude propulsion thruster branch being used for pointing were clogging, so the team switched to the second branch. When that branch showed signs of clogging in 2018, the team switched to the trajectory correction maneuver thrusters and have been using that branch since then.
Now those trajectory correction thruster tubes are even more clogged than the original branches were when the team swapped them in 2018. The clogged tubes are located inside the thrusters and direct fuel to the catalyst beds, where it is turned into gases. (These are different than the fuel tubes that send hydrazine to the thrusters.) Where the tube opening was originally only 0.01 inches (0.25 millimeters) in diameter, the clogging has reduced it to 0.0015 inches (0.035 mm), or about half the width of a human hair. As a result, the team needed to switch back to one of the attitude propulsion thruster branches.
Warming Up the Thrusters
Switching to different thrusters would have been a relatively simple operation for the mission in 1980 or even 2002. But the spacecraft’s age has introduced new challenges, primarily related to power supply and temperature. The mission has turned off all non-essential onboard systems, including some heaters, on both spacecraft to conserve their gradually shrinking electrical power supply, which is generated by decaying plutonium.
While those steps have worked to reduce power, they have also led to the spacecraft growing colder, an effect compounded by the loss of other non-essential systems that produced heat. Consequently, the attitude propulsion thruster branches have grown cold, and turning them on in that state could damage them, making the thrusters unusable.
The team determined that the best option would be to warm the thrusters before the switch by turning on what had been deemed non-essential heaters. However, as with so many challenges the Voyager team has faced, this presented a puzzle: The spacecraft’s power supply is so low that turning on non-essential heaters would require the mission to turn off something else to provide the heaters adequate electricity, and everything that’s currently operating is considered essential.
Studying the issue, they ruled out turning off one of the still-operating science instruments for a limited time because there’s a risk that the instrument would not come back online. After additional study and planning, the engineering team determined they could safely turn off one of the spacecraft’s main heaters for up to an hour, freeing up enough power to turn on the thruster heaters.
It worked. On Aug. 27, they confirmed that the needed thruster branch was back in action, helping point Voyager 1 toward Earth.
“All the decisions we will have to make going forward are going to require a lot more analysis and caution than they once did,” said Suzanne Dodd, Voyager’s project manager at the Jet Propulsion Laboratory which manages Voyager for NASA.
The spacecraft are exploring interstellar space, the region outside the bubble of particles and magnetic fields created by the Sun, where no other spacecraft are likely to visit for a long time. The mission science team is working to keep the Voyagers going for as long as possible, so they can continue to reveal what the interstellar environment is like.
News Media Contact
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov
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Last Updated Sep 10, 2024 Related Terms
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By NASA
AMS-02 mounted on the outside of the space station.NASA Visible matter in the form of stars and planets adds up to about five percent of the total known mass of the Universe. The rest is either dark matter, antimatter, or dark energy. The exact nature of these substances is unknown, but the International Space Station’s Alpha-Magnetic Spectrometer or AMS-02 is helping to solve the mystery.
AMS-02 collects data on charged particles from cosmic ray events, which helps scientists understand the origin of those rays and could ultimately reveal whether dark matter and antimatter exist.
To date, the instrument has collected data on about 573 events per second on average – just over 18 billion per year. This high volume of data enables highly precise statistical analyses, and multiple groups of researchers independently process the raw data to ensure accurate results.
Learn more about astrophysics research on the space station.
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